View full sizeIn this Monday, Sept. 24, 2001, file photo, rescue workers examine the site of the Sept. 11, 2001 World Trade Center terrorist attacks in New York. Several experts say there's no hard evidence to support the federal government's declaration this month that 50 kinds of cancer could be caused by exposure to World Trade Center dust. (AP Photo/Ted S. Warren, Pool, File)

NEW YORK — Several experts say there's no hard evidence to support the federal government's declaration this month that 50 kinds of cancer could be caused by exposure to World Trade Center dust.

The decision could help hundreds of people get payouts from a multibillion-dollar World Trade Center health fund to repay those ailing after they breathed in toxic dust created by the collapsing twin towers on Sept. 11, 2001.

But scientists say there is little research to prove that exposure to the toxic dust plume caused even one kind of cancer. And many acknowledge the payouts to cancer patients could take money away from those suffering from illnesses more definitively linked to Sept. 11, like asthma and some types of lung disease.

"To imagine that there is strong evidence about any cancer resulting from 9/11 is naive in the extreme," said Donald Berry, a biostatistics professor at the University of Texas MD Anderson Cancer Center in Houston.

Yet this month, Dr. John Howard, who heads the federal agency that researches workplace illnesses, added scores of common and rare cancers to a list that had previously included just 12 ailments caused by dust exposure.

Lung, skin, breast and thyroid cancer were among those added; of the most common types of cancer, only prostate cancer was excluded.

"We recognize how personal the issue of cancer and all of the health conditions related to the World Trade Center tragedy are to 9/11 responders, survivors and their loved ones," Howard said in a June 8 statement.

He declined requests for an interview with The Associated Press. His decision, based on an advisory panel's recommendation, will go through a public comment period and additional review before it's final.

Several factors about the decision by the National Institute for Occupational Safety and Health raised eyebrows in the scientific community:

— Only a few of the 17 people on the advisory panel are experts at tracking cancer and weighing causal risks; they were outnumbered by occupational physicians and advocates for Sept. 11 rescue and cleanup workers.

— Exposure to a cancer-causing agent doesn't necessarily mean someone will develop cancer. And if they do, conventional medical wisdom says it generally takes decades. But the panel agreed to cover those diagnosed with cancer within just a few years of the disaster.

—The panel members favored adding cancers if there was any argument to include them. They added thyroid cancer because a study found a higher-than-expected number of cases in firefighters who responded to 9/11, even though thyroid cancer is generally linked to genetics or high doses of radiation. The same study found a lower-than-expected number of lung cancers, but it was added because it was considered a plausible consequence of inhaling toxins at the site.

Even lawyers for the first responders were stunned: They had expected to see only certain blood and respiratory cancers put on the list.

"I understand the urge to want to compensate and reward the heroes and victims of that tragedy," said Dr. Alfred Neugut, a Columbia University oncologist and epidemiologist. But "if we're using medical compensation as the means to that, then we should be scientifically rigorous about it."

When the twin towers collapsed, much of lower Manhattan was enveloped in a dense cloud of pulverized glass and cement that left people in the area gasping for air. Fires smoldered in the rubble pile for weeks. Many workers labored in the ash wearing only flimsy paper masks, and went home coughing up black phlegm. Years later, some were still experiencing mild respiratory problems.

After Sept. 11, the government established the Victim Compensation Fund, which paid out about $7 billion for the nearly 3,000 deaths from the attacks and for injuries, including some rescuers with lung problems.

In late 2010, Congress set up two programs for anyone exposed to the rubble, smoke and dust at ground zero: rescue and cleanup workers and others who worked or lived in the area. Cancer was initially excluded, but Congress ordered periodic reviews based on the latest scientific evidence.

One $1.55 billion program is for treatment for any illness determined to be related to ground zero. The second $2.78 billion fund is to compensate people who suffered economic losses or a diminished quality of life because of their illness. Both programs expire in 2016, but could be extended.

How many people might apply isn't clear. In the decade since the attacks, about 60,000 people have enrolled in the two health programs for those who lived or worked within the disaster zone of lower Manhattan. Many have signed up for medical monitoring, but around 16,000 have been getting treatment annually.

Applicants could qualify for treatments and payments as long as they and their doctors make a plausible case that their disease was connected to the caustic dust.

Overall, roughly 1 in 2 men and 1 in 3 women will get cancer over their lifetimes. And generally, the more you look for cancer, the more cases you find. People worried that they got sick from the World Trade Center attacks are likely going to doctors more than other people. So some slow-growing cancers that started before 9/11 but were found afterward could end up being blamed on the fallout.

Reggie Hilaire was a rookie police officer when the hijacked planes flew into the World Trade Center. He spent the initial weeks after the attacks patrolling Harlem, miles away from the disaster zone, then was sent to Staten Island, where he spent weeks at a city landfill sorting through rubble and looking for human remains.

At the landfill, he wore a Tyvek suit, boots, gloves and a respirator to protect him. Months later, he also worked as a guard near ground zero, wearing no protective gear but never working on the debris pile itself.

Hilaire didn't develop the hacking cough or other problems experienced by those who inhaled big doses of soot. But he worried about his health, periodically visiting doctor's offices and clinics.

In 2005, at age 34, a lump showed up in his neck. He was diagnosed with thyroid cancer and successfully treated. Months later, he got more bad news: Doctors noticed he was anemic and investigated, leading to diagnosis of a second cancer — multiple myeloma, a blood cancer normally seen in the elderly.

Since roughly half of people with the diagnosis never get sick from it, doctors monitor a patient's condition rather than put them through chemotherapy and other difficult treatments — which is the case with Hilaire, still on the force. His medical bills have been covered by insurance, and to date, he hasn't applied for compensation from the federal fund.

View full sizeIn this Thursday, June 14, 2012 photo, NYPD Officer Reggie Hilaire, 41, poses for a picture in New York. Hilaire spent time looking for human remains right after the Sept. 11, 2001, terrorist attacks and later developed multiple cancers. Several experts say there's no hard evidence to support the federal government's declaration this month that 50 kinds of cancer could be caused by exposure to World Trade Center dust. (AP Photo/Seth Wenig)

Doctors don't know what causes multiple myeloma, but say genetics plays a role and that it is more common in black men. Hilaire, who is black, is convinced that toxins at ground zero are to blame.

"I've had cancer twice since 9/11, and I'm 41 years old," he said. "It would be some coincidence."

The U.S. government traditionally has been cautious about labeling things as cancer-causing agents, choosing to wait for multiple studies to confirm and reconfirm such a conclusion.

The famed 1964 surgeon general's report that permanently tied smoking to lung cancer came out more than a decade after a series of studies showed the link. The Environmental Protection Agency has taken decades to decide about other carcinogens. Howard's agency, NIOSH, has a conservative reputation as well.

But with this decision, Howard broke from that history.

"I think this was a special case," said Richard Clapp, a professor emeritus of environmental health at Boston University.

No question, bad stuff was in the air and on the ground. Asbestos, lead, mercury, PCBs and dioxins were all found at the smoldering World Trade Center site for months after the terror attacks. Dioxins have been associated with promoting the growth of some pre-existing cancerous cells, Clapp noted.

Previous studies have shown some of the contaminants — like asbestos, arsenic and soot, for example — have led to cancers in workers exposed to hefty amounts for long periods of time.

The fallout was a terrible mixture of toxins with significant potential to harm people, said Elizabeth Ward, an American Cancer Society vice president and cancer researcher who headed the advisory panel that made the recommendation to Howard.

"This was a really unique exposure," said Ward. Based on the best available evidence, the panel decided it was likely that people could get cancer, she said, and that it was better to offer help now than when it was too late.

Indeed, Howard and Ward have a number of supporters in the public health and scientific community who think it was the wisest decision, given the large human need. "I think for Dr. Howard, it's a very tough decision to make. I'm sure he knew that whatever he said, people are going to complain about it," said Daniel Wartenberg, an epidemiology professor at the University of Medicine & Dentistry of New Jersey.

"In my view, I hope he is wrong. I hope no one gets sick," he added.

A mere two years after 9/11, former New York City police detective John Walcott, 47, was successfully treated for a common type of leukemia that doesn't hit most people until about age 60.

Walcott arrived at the World Trade Center just after the second tower fell and spent months searching for human remains — on the pile, in empty buildings nearby, and later at the city landfill where the rubble had been taken.

He was so sure his cancer would eventually be covered by the federal program, he dropped his negligence lawsuit against the city last winter, as was required to remain eligible for the fund. He is well aware that some scientists question whether illnesses like his were really caused by ground zero toxins. But he has no doubts.